Superalloy articles such as blades and vanes are extensively used in gas turbine engines. Such articles have high mechanical properties and are resistant to oxidation and corrosion. Despite these good properties the severe operating environment which these parts operate can cause surface degradation in the form of cracks, areas of surface erosion, and the like. These components are expensive to produce and there is a need for repair processes to restore used articles to their original condition. Also, in the manufacturing process, defects occasionally occur and there is a similar need and desire to repair manufacturing defects.
Attempts have been made to weld repair these articles by applying filler material using electric arc welding. This approach has been generally unsuccessful because of cracking and because some superalloy compositions cannot be produced in wire or rod form.
It has also been proposed to cut away the defective areas and to braze in replacement sections having appropriate contours. This has not been found to be practical because of the wide variation in the size and shape of defects. Also, the trend in modern superalloy articles is toward thin wall castings having internal cooling passages. Use of a braze insert repair process with thin wall castings is inappropriate because of the likelihood that these thin walls will be completely cut through in the repair process.
Another repair process is described in U.S. Pat. No. 4,008,844 which is assigned to the present assignee and which is incorporated herein by reference. According to this patent a mixture of metal powders is made of two powders of different compositions. One composition approximates that of the superalloy to be repaired while the other composition also approximates the composition of the superalloy to be repaired, but contains a melting point depressant, usually boron. The defect to be repaired is filled with a mixture of these powders and then heated to a temperature at which the boron containing powder melts, but the boron-free powder and the substrate, does not melt. Solidification then occurs isothermally over a prolonged period of time as the boron diffuses into the substrate thereby raising the melting temperature. This is a successful process but has limitations in that it is difficult to apply exactly the right amount of material to a shallow surface defect and because when large defects are to be filled the molten material tends to flow out of the defect during the heat treatment process.
Accordingly, it is an object of the present invention to describe a surface flaw repair process applicable to superalloy components.
It is another object to describe a surface defect repair process which is particularly suited for repairing large shallow defects and for building up worn surfaces on superalloy components.
Yet another object of the present invention is to describe a surface defect repair process in which the previously encountered difficulties with the flow of molten filler materials are eliminated.